My golden rule is "Keep a safe note of all of your DNS records"
- Before a DNS record change
- After a DNS record change
- Before handing over or accepting DNS registration
- Before and after name server changes
- If you haven't looked at them for six months
- Any time.
KEEP A RECORD.
Some of the greatest issues that impact online services stem from mistakes around DNS. For the most part DNS is a very simple service. If something happens to change or incorrectly update your DNS records it can take hours or days for corrections to propagate but that process is held up if you have reestablish everything that you had records for (where is your email hosted, who holds your website? etc.) .
What do you do if you have been handed a domain to assist with where you were not previously involved and the customer does not have a record of what their DNS records were? I'm not infrequently ask to assist in situations like this. In the past this has meant a lot of keyboard work and information gathering.
A great service I have discovered recently is Security Trails (https://securitytrails.com/) who offer information on currently over 900 million host names including many historic DNS records. Their information has already saved me hours assisting customer recover "Forgotten" DNS records.
Please Note - Not sponsored or promoted content. Just very grateful at the amount of time Security Trails has saved me.